1. Field of the Invention
The present invention relates to a midair semiconductor device and a manufacturing method of the same.
2. Description of the Related Art
In an FBAR (Film Bulk Acoustic Resonator) filter, a MEMS (Micro Electro Mechanical Systems), and so on, a sealing structure is adopted to protect an element part from an external influence as in the case of a normal semiconductor device. These devices need to maintain a portion above the element part in a midair state in terms of their element characteristics. For this purpose, it is necessary to use a midair sealing structure. As such a sealing structure, a conventionally used can-type package is known, but since an increase in the size of the package is inevitable, it cannot possibly meet a demand for miniaturization.
Concerning this point, a circuit element in which a front surface of a Si substrate is covered with a porous resin layer in such a manner that only a portion above an element part which functions as a SAW filter is brought into a midair state is known (See Japanese Patent Laid-open Application No. Hei 6-283619, for example). Such a sealing structure has a problem of being inferior in the formation of the midair state. Further, since the porous resin layer shows absorbency, this sealing structure has a problem that it is difficult to ensure reliability of the element part.
As another sealing structure, a structure in which a SAW chip is flip-chip connected onto a Si substrate and the outside of the SAW chip is sealed with a Si cap having a C-shaped cross section is known (See Japanese Patent Laid-open Application No. 2001-110946, for example). This sealing structure needs the Si cap having a concave shape capable of housing the SAW chip. The cost required to fabricate such a Si cap becomes a factor that increases the manufacturing cost of a package. Therefore, it cannot be said that this sealing structure is practical. Moreover, since the Si cap is bonded to the Si substrate with a resin-based adhesive, the absorbency of an adhesive layer becomes a factor which reduces reliability, similarly to the sealing structure in which the element part is covered with the resin layer.
On the other hand, in Japanese Patent Laid-open Application No. 2001-068616, a wafer package in which a micro device provided on a base substrate is sealed with a cap substrate is described. Here, by bonding sealing members which are respectively formed on peripheral edges of the base substrate and the cap substrate, a hermetically sealed space is formed around the micro device. Further, by connecting a connection via formed in the cap substrate to an electrode on the base substrate side, a wire of the micro device is drawn to the outside of the package. As materials for forming the electrode, a connection surface (contact) of the connection via, and the sealing members, Si, In, Al Cu, Ag, an alloy and a compound thereof, and so on, which can be bonded to each other, are used.
In the above-described package, in the process of bonding of the base substrate and the cap substrate, the electrode of the base substrate and the contact of the connection via of the cap substrate, and the sealing members of the base substrate and the cap substrate need to be bonded simultaneously. Hence, there is a possibility that the electrical reliability between the electrode and the connection via, or the hermeticity of the sealed space deteriorates depending on the forming materials and bonding conditions. As just described, the conventional midair semiconductor devices have a problem that the connection reliability for the electrode of the element part and the hermeticity of the sealed space tend to deteriorate. Further, any of the conventional sealing structures has a disadvantage of being incapable of tuning from the rear surface side of the element part.